In a general wireless communication system, only one carrier is considered even though an uplink and downlink are set to different bandwidths. For example, an uplink and downlink are respectively configured with one carrier and bandwidths of the uplink and downlink are symmetrical on a single carrier basis in a wireless communication system.
ITU (International Telecommunication Union) requires a candidate technology for IMT-Advanced to support an extended bandwidth compared to the existing wireless communication system. However, it is difficult to allocate a frequency with a wide bandwidth in general. Accordingly, carrier aggregation, bandwidth aggregation or spectrum aggregation is developed which physically combines a plurality of bands in a frequency domain to create an effect of using a logically wide band in order to use segmented narrow bands.
Carrier aggregation is introduced in order to support increased throughput, prevent cost increase due to introduction of broadband RF elements and guarantee compatibility with existing systems. This carrier aggregation enables data exchange between a user equipment (UE) and a base station (BS) by combining a plurality of carriers on a bandwidth basis, defined in a conventional wireless communication system (e.g. a 3GPP LTE release 8 or 9 system in the case of a 3GPP LTE-Advanced system). Here, the carrier defined in the conventional wireless communication system can be referred to as a component carrier (CC). Carrier aggregation, wherein one or more CCs are used on each of an uplink and downlink, can be used. The carrier aggregation can include technologies that support system bandwidths of up to 100 MHz corresponding to a group of five CCs even if a single CC supports a bandwidth of 5 MHz, 10 MHz or 20 MHz.